PHOENIX – Former Senate Majority Leader George Mitchell warned baseball owners that a lack of cooperation with his investigation into steroid use will "significantly increase" the chances of government involvement.

Speaking to owners at baseball's quarterly meetings, Mitchell said he intends to interview active players and raised the possibility that Congress or other government authorities could compel testimony.

"I believe it will be in your best interests, and the best interests of baseball, if I can report that I have received full cooperation from your organizations, and from others, in conducting this investigation," Mitchell said in remarks that were released to reporters.

Mitchell cited last week's Hall of Fame vote to underscore the importance of his investigation. Mark McGwire was picked on 23.5 percent of ballots — far below the necessary 75 percent needed for induction. The vote was viewed by many as the first referendum on how history will judge an age when bulked-up players came under suspicion of using performance-enhancing drugs. Baseball didn't ban steroids until after the 2002 season.

"If nothing else, the results of the Hall of Fame voting last week, and the reaction to it, offer fresh evidence that this issue will not just fade away," Mitchell said. "Whether you think it fair or not, whether you think it justified or not, Major League Baseball has a cloud over its head, and that cloud will not just go away."

Mitchell cannot compel testimony. He warned the clubs that Congress or other federal or state authorities which do have subpoena power could get involved.

"I believe that a report that is not credible and thorough will significantly increase the possibility of action by others, especially if it's the result of a lack of cooperation by the clubs, or by anyone else who is or has been involved with baseball," Mitchell said.

Mitchell did not speak to reporters after addressing owners. He was hired by commissioner Bud Selig last March following more than a year of allegations against Barry Bonds, McGwire and other stars. No timetable was set for Mitchell's report.

Bonds is under investigation by a federal grand jury as to whether he perjured himself when he testified in 2003 in the BALCO steroid distribution case that he hadn't knowingly taken any performance-enhancing drugs.

The San Francisco Giants are negotiating a contract with Bonds, who needs 22 home runs to surpass Hank Aaron's mark of 755. Speaking to reporters at a golf tournament in the Dominican Republic this week, Bonds declined to discuss ongoing negotiations with the Giants, or his reported positive test for amphetamines last year. Giants owner Peter Magowan declined to answer questions about Bonds.

Selig also spoke to the owners about Mitchell's investigation. Asked if he had urged the clubs to cooperate with Mitchell, Selig said, "Urge is probably not strong enough."

"Look, some clubs have been more cooperative than others, but at this stage, I'm not concerned about that," Selig said. "He will have cooperation."

Selig would not say which clubs are lagging in their cooperation. Mitchell acknowledged that teams aren't used to dealing with "large-scale document discovery," which can be time-consuming. But he said his investigation would move faster if clubs cooperated more quickly.

"Many have asked when my report will be completed," he said. "The pace of this investigation is dictated by the rate at which information is received."

"It's a process that's very complicated, and it's just going to take time to complete," McLane said. "The steroids issues continue to emerge, and the public wants to know. For some reason they want to know more about baseball on steroids than they do football or basketball. So it's certainly focused on this."

During the meeting, Selig also spoke about the free-agent market and singled out the Chicago Cubs and San Francisco Giants, among others, for their spending, one official at the meeting said, speaking on condition of anonymity because the remarks during the session were not intended to be made public. Selig also mentioned the Toronto Blue Jays, the official said.

Selig wouldn't specify what he said to owners about the game's economics.

"We discussed some things, but we do that at every meeting," Selig said.